One example of a conventional shank attachment device is shown in FIG. 9 (Patent Document 1). A shank attachment device 61 shown in FIG. 9 is configured to attach a core drill 62 to a rotating portion of a drill device (not shown), and includes an arbor 63 and a shank 64. An attachment shaft 63a formed on the arbor 63 is detachably attachable to the rotating portion of the drill device. The arbor 63 and the shank 64 are detachably attachable to each other. The shank 64 is coupled to the core drill 62.
In a state where the shank 64 is attached to the arbor 63, a stopper steel ball 65 disposed on the arbor 63 engages with a stopper concave portion 66 formed on the shank 64. Since the stopper steel ball 65 and the stopper concave portion 66 engage with each other, a movement of the shank 64 in an axial direction away from the arbor 63 can be stopped, and the rotational torque of the arbor 63 can be transmitted to the shank 64 and the core drill 62.
Moreover, in the conventional shank attachment device 61 shown in FIG. 9, a center drill attachment hole is formed in the arbor 63, and a base end portion of a center drill 67 is inserted into the center drill attachment hole. The base end portion of the center drill 67 is fixed to the arbor 63 by a fixing screw 68, and the fixing screw 68 threadedly engages with a fixing screw hole formed on the arbor 63.    Patent Document 1: Japanese Laid-Open Patent Application Publication 2002-192412